PLEASE SIR SOLVE THE PROBLEM BY USING INTEGRATION OR USING SOME STANDARD RESULT AS I CANT UNDERSTAND THE SOLUTION GIVEN BY ALL ONLINE COACHING CENTER SOLUTIONS.PLEASE HELP SIR.HERE IS THE LINK http://www.goiit.com/posts/list/mechanics-solve-it-1015155.htm

Derivation Of Electric Field Due to One Hemisphere.

σ=Q/2πR²

4π Solid Angle Corresponds To Q/ε₀ Flux.............................From Gauss's Theorem

2π Solid Angle Will Correspond To Q/2ε₀ Flux

Q/2ε₀=E2πR²

E=Q/(2ε₀2πR²)

E=σ/2ε₀

Force= F= Edq..........................(F applied will be used to counteract this force)

dq=dAσ

F=(σ/2ε₀)(dAσ)

P=F/dA=σ²/2ε₀

Force Due To One Hemisphere On Other

=PπR².........................(πR² because we are calculating force on the rim of other hemisphere)

=(σ²/2ε₀)πR²

=πR²σ²/2ε₀

Approved